1. Field of the Invention
The present invention relates, in general, to rodless cylinder actuators for feeding workpieces in machining tools and, more particularly, to a rodless cylinder actuator having a piston slidably positioned within the cylinder, the piston being pnewmatically hydraulically reciprocable within the cylinder, thus reciprocating a slide table installed outside the cylinder housing.
2. Description of the Prior Art
A conventional rodless cylinder actuator for feeding workpieces in machining tools may be referred to Japanese Patent Laid-open Publication No. Sho. 62-266,206 published on Nov. 19, 1987.
FIGS. 1 to 4 show the above Japanese rodless cylinder actuator. As shown in the drawings, the actuator 1 has a slit 3 that longitudinally extends from one end to the other end on its top surface of the cylinder 1. A longitudinal bore 2 is formed within the cylinder 1 and communicates with the outside of the cylinder 1 through the slit 3. A piston 4, consisting two piston bodies 5, is slidably received within the bore 2. Each of the two piston bodies 5 has a circumferential groove 6 on its external surface, with a sealing member 7 being set in the groove 6 to be brought into close contact with the interior surface of the bore 2.
A longitudinal groove 26 is formed along each top edge of the slit 3. The width of each groove 26 is narrower than that of the slit 3. A longitudinal subsidiary sealing strip 27 is set into the grooves 26 at both side edges thereof, thus sealing the top portion of the slit 3. A movable block 11 is slidably received within the bore 2. The movable block 11 is integrated with a connection block 14 at its top section, with a guide groove 28 being formed on the top surface of the connection block 14. A guide surface 29 is formed on the bottom of the guide groove 28. The above guide surface 29 is brought into contact with the lower surface of the subsidiary sealing strip 27, thus allowing the strip 27 to escape from the grooves 26. On the other hand, two pressure plates 30 are provided at both sides of the connection body 14. The above pressure plates 30 come into contact with the top surface of the subsidiary sealing strip 27, thus pressing down the strip 27 into the grooves 26. A sealing strip 19 is positioned within the lower portion of the slit 3 while being set in a groove 16 formed in the lower portion of the slit 3. A rail 20 is longitudinally formed along the central axis of the top surface of the sealing strip 19. The above sealing strip 19 is also fitted into the lower portion of the slit 3 at the rail 20.
A cap 31, having an air hole 32, is tightened to each end of the cylinder 1. An air pipe 33 extends from the inside end of each cap 31 while communicating with the air hole 31. The above air pipe 33 is designed to be selectively inserted into a relief hole 34 formed on each piston body 5. Each end of the two sealing strips 19 and 27 is mounted to the junction between the cap 31 and a mount plate 36 using a pin 37. In such a case, the mount plate 36 is provided on the top surface of the subsidiary sealing strip 27. A slide table 38, carrying a workpiece thereon, is seated on and mounted to the connection body 14 using a plurality of pins 39.
The above rodless cylinder actuator 1 is operated as follows. When pressurized air is applied to the rear chamber 40 of the piston 4, with the front chamber 42 of the piston 4 discharging air therefrom, a pressure difference is generated between the two chambers 40 and 42. The piston 4 is thus moved forwardly within the cylinder 1. When the piston 4 moves forwardly as described above, two elastic protrusions 21 of the sealing strip 19 are elastically deformed to be removed from two protrusion rails 17 of the cylinder 1, thus allowing the sealing strip 19 to be removed from the groove 16. The strip 19 is inserted into a passage 24 at its front portion.
As both the piston 4 and the movable body 11 further move forwardly within the bore 2 of the cylinder 1, the rear piston body 5 pushes the sealing strip 19 into the groove 16, thus allowing the protrusions 21 to engage with the protrusion rails 17 while elastically deforming the protrusions 21 of the sealing strip 19.
On the other hand, when pressurized air is applied to the front chamber 42 of the piston 4, with the rear chamber 40 discharging air, a pressure difference is generated between the two chambers 40 and 42. Both the piston 4 and the movable body 11 are thus moved backwardly within the cylinder 1. In such a case, the sealing strip 19 is removed from the groove 16 and is inserted into the passage 24 at its rear end. Therefore, it is possible for both the connection body 14 and the slide table 38 to be reciprocable along the slit 3. When the piston 4 and the movable body 11 are moved within the cylinder 1, the sealing strip 19 partially closes the strip 3 at a position free from the piston bodies 5. That is, at the position free from the piston bodies 5, the elastic protrusions 21 of the strip 19 engage with the protrusion rails 17 of the cylinder 1, thus closing the strip 3 at that position. Therefore, even when the internal pressure of the front or rear chamber 42 or 40 is reduced to a low pressure, the sealing strip 19 is free from sagging into the chamber 42 or 40, but completely closes and seals the slit 3 at the position around the chamber 42 or 40. Therefore, the sealing strip 19 almost completely prevents air leakage through the slit 3.
During a reciprocating motion of the connection body 14 along the slit 3, the leading portion of the subsidiary sealing strip 27 is partially raised up at its lower surface by the leading end of the guide surface 29 of the connection body 14, thus escaping from the grooves 26 of the slit 3 prior to being laid on the guide surface 29 of the body 14. On the other hand, the trailed portion of the sealing strip 27 is pressed down at its upper surface by a trailed pressure plate 30, thus being brought into engagement with the grooves 26 of the strip 3. Therefore, the slit 3 is always sealed by the subsidiary sealing strip 27 at the front and rear of the reciprocating connection body 14. It is thus possible to almost completely prevent an introduction of foreign substances, such as dust, into the cylinder 1 through the slit 3 during a reciprocating motion of the connection body 13 along the slit 3.
In addition, when the sealing strip 19 engages with the groove 16 of the slit 3, the lower surface of the sealing strip 19 may be somewhat protruded into the bore 2 as shown in FIG. 4 due to a designing tolerance of the strip 19 and the groove 16. In such a case, the chambers 40 and 42 may fail to be completely sealed, thus causing an air leakage between them. However, such an air leakage between the chambers 40 and 42 is completely prevented by a pressure contact between the sealing member 7 of the piston 4 and a thin plate 22 of the sealing strip 19. The sealing member 7 of the piston 4 is designed to be elastically extendible or contractible, while the thin plate 22 totally covers the lower surface of the sealing strip 19 while extending outside both side edges of the strip 19. Therefore, when the lower surface of the sealing strip 19 is protruded into the bore 2 as described above, the elastic sealing member 7 compresses both side edges of the thin plate 22, thus appropriately bending and deforming both side edges of the plate 22. The sealing member 7 is thus brought into close contact with both the inner surface of the bore 2 and the thin plate 22 without leaving a gap between them. Therefore, the actuator is free from air leakage between the chambers 40 and 42.
However, the above rodless cylinder actuator has the following problems. That is, it is necessary for the actuator to have a plurality of sealing members used for preventing air leakage within the cylinders. This complicates the construction of such actuators and increases the production cost of the actuators.
It is also necessary to precisely machine the sealing members, thus resulting in a further increase in the production cost of the rodless cylinder actuator. Due to the complex construction caused by the sealing members, the actuator is apt to be broken at the sealing members. This increases the maintenance and repairing cost of the actuator and reduces the expected life span of the cylinder.